Conventional optical transport networks are mainly in a ring or linear topology, and can provide a series of protection technologies such as multiplex section protection, channel ring protection, linear 1:1 multiplex section protection, linear 1+1 multiplex section protection, and end-to-end subnetwork connection protection (SNCP). When a conventional optical network protection technology can provide protection against a single-link fault, a protection resource that needs to be reserved in the conventional optical network protection technology occupies a large quantity of network bandwidth resources, causing low bandwidth utilization.
With the development of telecommunications technologies, a shared mesh protection (SMP) technology based on an automatically switched optical network (ASON) emerges. A most noticeable difference between the SMP technology and the conventional optical network protection technology is as follows. In the SMP technology, dynamic real-time trail recovery can be provided, without reserving a bandwidth resource for a protection trail, and real-time calculation can be performed based on a failed link or a failed node after a fault occurs, to determine the protection trail. In the SMP technology, to reduce a protection switching time, a protection switching message may be transferred by using an automatic protection switching (APS) overhead, so that protection switching of an entire service is implemented.
The International Telecommunication Union-Telecommunication Standardization Sector (ITU-T) G.ODUSMP standard specifies an APS overhead encoding format for implementing SMP protection switching. As shown in FIG. 1, FIG. 1 shows an APS overhead encoding format in the prior art. An overhead part of an APS message may be used to describe an SMP protection switching status, includes a total of 4 bytes that are equal to 32 bits, and describes the following three types of information.
A (1) Request is included in the 1st bit to the 4th bit, and represents a protection switching request type such as SF (Signal Failure), SD (Signal Degrade), RR (Reverse Request), NR (No Request), MS (Manual Switch), and FS (Forced Switch).
A (2) Requested Signal is included in the 9th bit to the 16th bit, represents a service ID (Identifier), for example, W1, of a service that requests a shared protection resource, and is set to all zeros when there is no request.
(3) Bridged Signal is included in the 17th bit to the 24th bit, represents a service ID, for example, W1, of a service for which bridging has been completed, and is set to all zeros when there is no service for which bridging has been completed.
For a definition of the foregoing encoding format, refer to the ITU-T G.ODUSMP standard. It can be seen from the encoding format in FIG. 1 that, because valid fields occupy only 20 bits and reserved fields occupy 12 bits, overhead field is not fully used, causing overhead resource waste.